1. Field of the Invention
The present invention relates to a color image forming apparatus, and more particularly, to a color image forming apparatus having a function of forming a mono-color image based on full-color image data.
2. Description of the Prior Art
Many color image forming apparatuses are provided with not only a function of forming a full-color image based on full-color image data which is a primary function thereof, but also a function of forming a mono-color image based on the full-color image data.
Full-color image data comprising red (R), green (G) and blue (B) signals of three primary colors of light is converted into full-color image data comprising yellow (Y), magenta (M) and cyan (C) signals of three primary colors of image &/rming material such as toner. In a color image forming apparatus, of the three primary color signals, a magenta signal is often used in forming a mono-color image based on the full color image data. This is because of the fact that it is considered that the luminosity of the human eye is sensitive to a color component of green.
As described above, in the conventional color image forming apparatus, a mono-color image is formed based on only the signal data of one color. In this case, there is hardly any problem when an original includes green images. However, for images of colors other than green, the density of the mono-color image formed is low which causes the image to be weak in color since yellow and cyan signal data are not used. In an extreme case, a defective image is formed.